1. Field of the Invention
The present invention relates to the apparatus for measuring a thickness of a paint film according to an information concerning a dynamic levelling property of a paint film surface in a wet state immediately after an application of the paint medium.
2. Description of the Background Art
The known examples of a conventional apparatus for measuring a thickness of a paint film include a contact type utilizing a needle gauge, and a non-contact type utilizing an electromagnetic property or an eddy current.
However, the contact type paint film thickness measurement apparatus utilizing a needle gauge has been associated with a serious problem concerning a possible damage on the paint film surface due to the contact between the needle gauge and the paint film surface, which severely affects the quality of painting.
Moreover, such a contact type paint film thickness measurement apparatus is apparently inapplicable to the measurement of the wet paint film thickness.
On the other hand, in a conventional non-contact type paint film thickness measurement apparatus utilizing the non-magnetic property of the paint medium, the measurement of the paint film thickness can be made in a non-contacting manner as shown in FIGS. 1A and 1B.
Namely, as shown in FIG. 1A, a non-contact type film thickness sensor 82 is positioned in advance at a prescribed small gap h.sub.0 from a painting surface of a painting target body 81, such that the magnetic field is generated between the paint target body 81 and the non-contact type film thickness sensor 82 by a transmitter and receiver coil provided within the non-contact type film thickness sensor 82. Then, as shown in FIG. 1B, when a paint medium 83 is applied onto the painting surface of the painting target body 81 for a thickness "h", the attenuation of the magnetic field between the painting target body 81 and the non-contact type film thickness sensor 82 after the painting due to the electromagnetic resistance of the applied paint medium can be detected by the non-contact type film thickness sensor 82 which detects the change of the magnetic flux that is inversely proportional to the thickness "h" of the paint film.
However, in such a conventional non-contact type paint film thickness measurement apparatus, there is a need to set up the prescribed small gap between the painting target body 81 and the non-contact type film thickness sensor 82 before the actual painting is made, but this small gap is so small that there is a potential danger for the non-contact type film thickness sensor 82 to actually make a contact with the paint film surface and damage the paint film surface.
Moreover, this conventional non-contact type paint film thickness measurement apparatus has also been associated with the inconveniences concerning the facts that the measurement cannot be initiated after the painting is made, and that two measurements before and after the painting are necessary in order to obtain the paint film thickness.
Furthermore, this conventional non-contact type paint film thickness measurement apparatus has also been associated with the basic problem that the measurement accuracy has been so poor that the application to the measurement of the thin wet paint film has been quite difficult.
Now, the measurement of the thickness of the paint film using such a paint film thickness measurement apparatus is most typically utilized for the purpose of the management of the quality of painting, while the management of the quality of painting is usually made on a basis of a thickness of the paint film in a dry state obtained by a drying process after the painting process, so that the conventional paint film thickness measurement apparatus is usually required to measure only the dry paint film thickness.
However, this manner of management of the quality of painting has a consequence that the measurement of the paint film thickness can be carried out only after the several hours of drying process after the painting process, so that the data on the paint film thickness is unavailable during the painting process itself.
As a consequence, the data on the paint film thickness could not have been fed back to the painting process itself for the purpose of appropriately controlling the painting conditions used in the painting process according to the resulting paint film thickness. Therefore, even when an inappropriate paint film thickness is detected by the measurement made after the drying process, there are cases in which the entire painting process is required to be carried out again from the beginning such that the earlier painting is totally wasted.
On the other hand, in such management of the quality of painting, it is also necessary to check the presence of the sagging on the paint film, especially on vertical paint surfaces. Conventionally, the checking of the presence of the sagging has been achieved by the human eye inspection by the inspection worker at a painting process site.
However, in the usual painting process, there are many aspects to be inspected by the inspection worker, so that it is desirable to provide means for automatically checking the presence of the sagging such that either the work load of the inspection worker can be reduced or a number of inspection workers required in the painting process can be reduced.